1. Field of the Invention
The present invention relates to a communication system which operates under a multi-access environment where a plurality of mobile terminals simultaneously communicate with a single cell station. In particular, the present invention relates to a communication system which can overcome the problem of a cell station becoming overloaded as the number of such mobile terminals increases.
More specifically, the present invention relates to a communication system which can overcome the problem of it becoming more difficult to efficiently layout cell stations in the service area and to successfully carry out routing as cells become smaller. More particularly, the present invention relates to a communication system which allows the network of installed cell stations to be dynamically reconfigured according to their respective locations.
2. Description of the Related Art
Mobile communication dates back to the discovery of electromagnetic waves, and since then, it has been studied and developed as means for communication on boats and ships, aircraft, and trains. Mobile communication is now widespread as means for communication with or among vehicles and persons. Even multimedia content such as computer data and images can be transmitted, in addition to characters and voice by conventional telegraph and telephone.
Recently, mobile terminals are becoming more compact and less expensive because of improved manufacturing engineering. Furthermore, more extensive information and communication services are promoting the personal use of mobile terminals such as cellphones. Deregulation of telecommunication services and reduction in communication charges are also contributing to an increase in the number of mobile users.
Mobile communication is basically achieved such that a mobile station, such as a car phone or a cellphone, transmits/receives radio waves to/from the nearest cell station found. A cell is defined as a communication range within which radio waves from a single cell station are available. A cell is typically formed as a circle with a certain radius and having the cell station antenna at its center. A communication service area is formed of such cells laid out continuously.
FIG. 22 schematically illustrates the layout of cells of a mobile radio communication system, such as a cellular system, in which the service area is covered by using a plurality of cell stations. As shown in FIG. 22, a large service area is formed by continuously laying out cells defined by cell stations (not shown) which are installed at a predetermined distance from each other.
The mobile communication system uses cells, each covering only a range within which radio waves from that cell station are available. This strategy allows the same frequency to be shared among cells, thus efficiently using limited frequency resources. This strategy also allows the output of radio waves for communication to be low, which is advantageous particularly for battery-driven mobile objects because low output of radio waves contributes to power saving and compact design of such mobile objects.
Recently, there has been a growing demand for cells which can accommodate as many users as possible and for efficient use of limited frequency resources, as the number of cellphone (cellular) users increases. One cell handles a plurality of mobile terminals, which simultaneously communicate with a single cell station. For this purpose, the cell station is required to multiplex radio signals to identify which signals belong to which users.
A conventional cell station having terminals connected thereto is a large facility covering a wide service area (cell). Thus, as the number of terminals increases, the same cell station has more terminals connected thereto; that is, the cell station is easily overloaded. The heavy load described above poses a problem in that the data transfer rate becomes low. In order to overcome this problem, smaller cells are usually used; however, smaller cells make it difficult to efficiently layout the cell stations in the service space and successfully carry out routing as the number of cell stations increases.